The present invention relates to a digital broadcast recording and reproducing apparatus for receiving, recording and reproducing television broadcasts of a digital format.
Although television broadcasts are presently provided in the analog format, it is considered that the analog television broadcasts will be successively replaced by digital television broadcasts (hereinafter, referred to as digital TV broadcasts) in the future because of the necessities of further improvement of image quality and increasing the number of broadcast channels.
In the digital TV broadcast, by compression-coding video signals, a multiplicity of channels can be secured within a limited frequency band. In a presently-proposed digital TV broadcast, an MPEG2 format which is a video signal compression coding format standardized by a working group of the moving picture experts group (hereinafter, referred to as MPEG) is used for compression-coding of the video signals. Video signals are compression-coded into coded data according to the MPEG2 format. The coded data of a multiplicity of channels (e.g. eight channels) are brought together into a bit stream which is a data string. The bit stream is modulated and transmitted as a digital broadcast signal.
On the other hand, for recording of television broadcasts at home, presently, a video tape recorder of the VHS format which is an analog format is mainly used (hereinafter, referred to as VHS format VTR). Moreover, recently, digital video tape recorders based on the DV format standardized by xe2x80x9cthe HD digital VCR conferencexe2x80x9d which is a conference for examining home digital VTR standards have been put on the market (hereinafter, referred to as DV-format VTR), so that high-image-quality recording has been possible.
FIG. 6 shows a system configuration in the case of recording, by the DV format VTR, a program of a digital TV broadcast received by use of a digital TV broadcast receiver 120 commercially available as xe2x80x9cSet Top Box.xe2x80x9d
In FIG. 6, reception signals of radio waves from a satellite received by an antenna 110 are input to an antenna input terminal 121 of the receiver 120 for receiving digital TV broadcasts. The signals input from the antenna input terminal 121 are demodulated by a tuner section 122, and a bit stream is output. From the bit stream, the data string of a desired channel is selected by a channel selection section 123, and the selected data string of the channel is decompression-decoded and put back into video signals according to the MPEG2 format by an MPEG2 decoder 124. The video signals are output to a video output terminal 125. Then, the video signals are input to a video recording input terminal 131 for inputting recording video signals of a DV format VTR 130. The input video signals are reproduced by way of an encoder 132 for video signal compression coding of DV-format (hereinafter, referred to as DV encoder), a recording and reproducing section 133 and a decoder 134 for decompression-decoding of DV-format video signals (hereinafter, referred to as DV decoder), and the reproduced video signals are output to a video reproduction output terminal 135. The reproduced video signals are displayed on a monitor image receiving apparatus 140.
The operation to record and reproduce a program of a digital TV broadcast to and from the format DV VTR in the above-described configuration will be described in detail hereafter.
Radio waves of a digital TV broadcast from a satellite are received by the antenna 110 and supplied to the receiver 120. At the receiver 120, the signals are received by the antenna input terminal 121 and demodulated by the tuner section 122 into a bit stream. The bit stream is input to the channel selection section 123 and the data string of a desired channel is selected. The selected data string is decompression-decoded by the MPEG2 decoder 124 and put back into video signals, and are output to the video output terminal 125. At the DV format VTR 130, the video signals are input from the video recording input terminal 131, compression-coded by the DV encoder 132, and recorded by-the recording and reproducing section 133.
At the time of reproduction, the signals reproduced by the recording and reproducing section 133 are decompression-decoded by the DV decoder 134, and the. resultant signals are output to the video reproduction output terminal 135. The signals are monitored by the image receiving apparatus 140.
The maximum recording time of DV format VTRs is 4 hours and 30 minutes when a standard cassette tape is used. Even when the thin tape for VHS VTRs is used in the three times mode, the maximum recording time is only 8 hours. Recording times of these lengths are insufficient to-record a multiplicity of programs on a multiplicity of channels of digital TV broadcasts by programming the VTR to do so by use of a timer in advance (hereinafter, referred to as timer recording).
In multi-channel digital broadcasts, since the number of programs broadcasted for a week is great, it is considered that a great number of programs are programmed to be recorded in one timer recording setting. Moreover, an occasion will be more likely to arise when programs on a plurality of channels broadcasted during the same time period are to be recorded at the same time. However, the present VHS format VTRs and DV format VTRs with short recording times cannot satisfactorily meet such a demand.
Therefore, paying attention to the fact that the compression rate of the MPEG2 format is much higher than that of the DV format, a method can be considered that uses an MPEG2-format VTR instead of the DV format VTR of FIG. 6 in order to increase the recording time. The recording rate of the DV format is 41.85 Mbits/second including sound and sub codes (see Nikkei Electronics Books xe2x80x9cData ashuku gijitsu (Data compression technology)xe2x80x9d, p144). On the contrary, when standard television signals are coded according to the MPEG2 format, the information amount is 6 to 8 Mbits/second (see Bulletin of the Institute of Image Information and Television Engineers, Vol. 50, No. 1 (1996), p40). Therefore, when an MPEG2-format VTR is used, recording can be performed for a time five to seven times longer. However, in the system configuration of FIG. 6, since MPEG2-format digital broadcast signals are decoded by the MPEG2 decoder 124 in the receiver 120 called Set Top Box, the signals decoded as data to be supplied to the MPEG2-format VTR are necessarily converted again to MPEG2-format signals by use of an MPEG2 encoder. Since the MPEG2 encoder requires very complicated signal processing compared with the MPEG2 decoder, the circuit scale thereof is enormous and is expensive. Therefore, at the present time, it is considerably difficult to employ this for home appliances in view of the cost.
Objects of the present invention are to solve the above-mentioned problems, to realize long-time digital recording without the use of the expensive MPEG2 encoder for recording and reproduction of the digital broadcasts, and moreover to realize a digital broadcast recording and reproducing apparatus capable of simultaneous timer-recording programs on a plurality of channels.
In order to meet the above-mentioned objects, a digital broadcast recording and reproducing apparatus according to the present invention comprises: a tuner section for demodulating a received compression-coded digital broadcast signal corresponding to a multiplicity of channels into a data string including coded data; recording channel selection means for selecting coded data of channels to be recorded from the above-mentioned data string, and outputting a formed data string; recording and reproducing means for recording and reproducing the data string output from the above-mentioned recording channel selection means; and a decoder for decompression-decoding the coded data of the data string reproduced by the above-mentioned recording and reproducing means, and outputting a video signal. According to this configuration, by recording the data string of the compression-coded digital broadcast signal to the recording and reproducing means, and decompression-decoding the reproduction output of the recording and reproducing means by a decoder, a long time digital recording of digital broadcasts can be performed without use of the encoder.
Furthermore, a digital broadcast recording and reproducing apparatus according to another aspect of the present invention comprises reproducing channel selection means. The reproducing channel selection means selects coded data corresponding to one target channel from the data string of a plurality of channels reproduced by the recording and reproducing means where the data string of a plurality of channels is recorded, and selectively outputs a formed data string to the decoder. According to this configuration, programs on a plurality of channels can be recorded onto one recording medium.
Furthermore, a digital broadcast recording and reproducing apparatus according to another aspect of the present invention comprises a plurality of tuner sections and recording channel selection means and comprises data string multiplexing means for multiplexing a plurality of pairs of data strings output from the recording channel selection means into one data string. According to this configuration, programs on a multiplicity of arbitrary channels can be recorded onto one recording medium.
Furthermore, the recording and reproducing means is magnetic recording and reproducing means for recording onto magnetic tape by a rotary head, and switching the running speed of the magnetic tape in accordance with the number of channels to be recorded, and according to this configuration, when the number of channels to be recorded is small, the recording time is increased and recording can be performed for a long time.
Furthermore, by performing recording of N times (N is the number of channels to be recorded) every M scannings by the rotary head (M is the maximum number of recordable channels), the track pitch is fixed even if the number of channels to be recorded is changed.
Furthermore, when N is a divisor of M, the magnetic recording and reproducing apparatus transports the magnetic tape at a constant speed of N/M times of the speed when the number of channels to be recorded is M, and performs recording once every M/N scannings by the rotary head. According to this configuration, intermittent recording intervals are fixed, so that the recording track pitch is fixed.
Furthermore, when N is not a divisor of M, recording is performed M times every M scannings by the rotary head, and the data string output from the recording channel selection means is recorded in N times therein. According to this configuration, the recording track pitch is fixed even when N is not a divisor of M.
Furthermore, when the number M in the magnetic recording and reproducing means is six or four, the case more frequently occurs where N is a divisor of M, so that the case more frequently occurs where intermittent recording can be performed at fixed intervals without any waste.
Furthermore, recording and reproducing means according to another aspect is magnetic recording and reproducing means configured so as to record an identification signal for identifying the number of channels to be recorded at the time of recording. According to this configuration, at the time of reproduction, the running speed of the magnetic tape can be switched so as to be the same as it is at the time of recording.
Furthermore, magnetic recording and reproducing means according to another aspect is configured so as to perform recording with the identification signal being changed immediately before the number of channels to be recorded is changed. According to this configuration, disturbance of reproduction can be prevented.
Furthermore, magnetic recording and reproducing apparatus according to another aspect comprises timer recording setting means, and is configured so that an alarm is provided when the number of channels which overlap in setting exceeds the maximum number of recordable channels of the recording and reproducing means. According to this configuration, misoperation of timer setting can be prevented.